Salmonella Sources: Vehicles of Contamination
Salmonella is the leading cause of bacterial foodborne illnesses in the United States, and is responsible for approximately 1.4 million non-typhoidal illnesses, 15,000 hospitalizations, and 400 deaths in the US annually. Salmonella is a zoonotic disease, and can be found in animals such as chickens, turkeys, pigs, cows, turtles, reptiles, and birds. These bacteria cause human illness when they are ingested, and can lead to Salmonella infection through various modes of transmission, including through food and water sources, animal-to-human contact, and person-to-person contact. One study found that 87% of all confirmed cases of Salmonella were foodborne, with 10 percent from person-to-person infection and 3% caused by pets. 
Salmonella is most commonly transmitted through contaminated food or water, and is often associated with the consumption of eggs or poultry products. According to the United States Department of Agriculture (USDA), between 30 and 35 percent of processed poultry is contaminated with Salmonella. One in ten thousand eggs produced in the northeastern United States is also said to be contaminated with Salmonella. Beyond poultry, ground beef, fresh produce, water, and ready-to-eat foods such as peanut butter, almonds, and snack foods, have all been associated with Salmonella outbreaks. Improper sanitation, cross-contamination, and a failure to cook meat and eggs to a high enough temperature to kill Salmonella have all been factors contributing to Salmonella outbreaks associated with restaurant food.
The introduction of pasteurization greatly reduced the number of foodborne illness outbreaks associated with milk and other dairy sources; however, the consumption of raw milk and unpasteurized cheeses remains a risk factor for Salmonella infection. Salmonella and other pathogens are shed in the feces of livestock such as cows and goats and can contaminate milk during the milking process.
Fresh fruits and vegetables can become contaminated before or after harvest. Contaminated seeds, irrigation water, and flooding have contributed to Salmonella outbreaks traced to sprouts, lettuce, and other fresh produce. Unpasteurized orange juice has been the source of several Salmonella outbreaks.
Water intended for recreation (e.g., pools, shallow lakes) and for human consumption can also become tainted with Salmonella. When lakes become contaminated with Salmonella, several weeks or months can be required for water quality conditions to improve or return to normal. Proper chlorination resolves Salmonella contamination issues in pools and municipal water systems.
Person-to-person transmission of Salmonella occurs through a fecal-oral route, and is particularly common among infants and young children who have not yet developed hygienic practices conducive to stopping the spread of Salmonella. Other person-to-person transmission of Salmonella has been known to occur between infected individuals and their caregivers, and between infected food handlers and people who consume the food they prepare.
- Centers for Disease Control and Prevention. 2008. Preliminary FoodNet Data on the Incidence of Infection with Pathogens Transmitted Commonly Through Food. Retrieved February 2, 2009.
- Buzby, Jean and Roberts, Tonya, “The Economics of Enteric Infections: Human Foodborne Disease Costs, GASTROENTEROLOGY, Vol. 136, No. 6, pp. 1851-62 (May 2009).
- United States Department of Agriculture. 2009. A Focus on Salmonella—Updated Version. Retrieved July 14, 2009